Underground storage



Oct. 2, 1962 G. w. SWINNEY 3,056,265

UNDERGROUND STORAGE Filed June 16, 1958 BY nkAscw Z A T TORNEVS Unite Ware Filed June 16, use, Ser. No. 742,342 7 Claims. or. 6r-.s

This invention relates to the underground storage of fluids such as gaseous ethylene, liquefied petroleum gases such as propane and butane, ammonia, and the like. In one aspect, it relates to methods and apparatus for controlling the filling of an underground storage cavern with product such as the aforementioned fluids.

Constantly expanding production of fluids for the industries of this country and elsewhere has created a definite problem in providing suitable storage facilities for these fluids. In petroleum industries, in particular, the problem of storage of fluids such as gaseous ethylene, liquefied petroleum gases such as propane and butane, ammonia, and the like, is presently an urgent one due to the high cost of storage in surface equipment, such as steel tanks, and due to the massive construction required to withstand the vapor pressure of such fluids. Also adding to the problem of adequate storage facilities is the fact that many industries, especially the liquefied petroleum gases industry, experience seasonal peak loads in the requirements for their products and corresponding seasonal slack periods. These fluctuations in requirements require large storage facilities and the advantages of storing fluids in underground caverns have lately become very attractive and important.

Underground storage caverns are generally formed in impermeable earth formations, either by conventional mining methods, or, in some cases, by dissolving out a soluble material with solvents to create a storage space in soluble formations, for example, in salt domes. The resulting caverns are less expensive to provide than would be an equal volume of orthodox surface space and have particularly proven their value in the storage of liquefied petroleum gases.

The instant invention is particularly concerned with those underground storage caverns formed in underground salt formations. This type of cavern is generally formed by drilling an access here from the surface of the ground down into a salt formation, such as a salt dome, and then washing out the salt by circulating fresh water down one conduit in the access bore to dissolve the salt, while continuously removing the resulting brine through another conduit in the access bore.

One of the problems involved in this type of storage is that of readily determining when the cavern is completely filled with product. These caverns are generally located hundreds or even thousands of feet below the surface of the ground in regions which are inaccessible to an observer. The access bore is, of course, relatively small in diameter and this limits the manner in which the amount of product stored in the cavern can be determined during filling operations. Then again, the cavern often has a generally irregular shape which itself presents problems. During storage, there generally will always be a pool of brine or other displacing medium, such as oil, in the bottom of the cavern and this further complicates the filling of the cavern with product. These caverns are generally filled by pumping the product into the cavern under suflicient pressure to displace the brine therein to the surface so as to conduct the same to a pond or reservoir. For some time there has arisen a need for an automatic method and apparatus for controlling the filling of the cavern with product to prevent any substantial amount of product from being discharged With the brine.

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Where the product to be stored is inflammable, such as propane, uncontrolled filling of the cavern with the product can result in discharge of the inflammable product along with the brine, thus creating a fire hazard, as well as the loss of valuable product.

Attempts to control the filling of the cavern by metering into and out of the cavern the product and displacing fluid have proven to be generally unsatisfactory because of errors in metering, especially Where the residual stored product and displacing fluid have remained undisturbed over relatively long periods during which losses to the formation and errors in metering calibration and storage recordation can occur. Then again, methods relying on sensory responses have also proven unreliable.

Accordingly, an object of this invention is to provide an improved method and apparatus for controlling the fi ling of an underground storage cavern with product, such as highly volatile or normally gaseous hydrocarbon materials. Another object is to store such fluid in an underground storage cavern in a safe, reliable, and eflicient manner. Another object is to control the interface level between product and displacing medium in an underground storage cavern, such as those caverns formed in an underground salt formation. Other objects and advantages of this invention will become apparent from the following discussion, claims, and drawings in which:

FIGURE 1 is a schematic elevational view in partial section of an underground storage cavern provided with the appurtenances necessary in controlling the filling of the cavern in accordance with this invention; and

FIGURE 2 is a partial View similar to FIGURE 1 showing a modification thereof.

Referring now to the drawing, a sealed underground storage cavern generally designated 10 is illustrated. This cavern 10 can be formed by methods well. known in the art. For example, a vertical access bore 11 is drilled from the ground through various overlying formations 12, such as surface soil, shale, limestone, sandstone, and the like, into a soluble impermeable formation 13, such as a salt formation or salt dome, this latter soluble formation generally having thereabove a layer of cap rock such as anhydrite or gypsum, and preferably drilling the access bore to the ultimate depth of the subsequently formed cavern. After drilling the access bore 11 into the salt formation 13, a casing '14 is set in the borehole and cemented at 16 to the surrounding formation so as to form a fluid-tight seal against the leakage of fluids past the casing and to securely anchor said casing. A pipe 17 such as an eductor or wash pipe, is inserted through casing 14 in spaced relation thereto, thereby forming an annulus 18, the lower end of the pipe 17 depending beneath the lower end of casing 14 and extending further into the access bore. Alternatively, another pipe (not shown) can be inserted in the borehole concentrically surrounding pipe 17, this other protective pipe depending below the bottom of casing 14 and above the lower open end of pipe 17 and serving to protect the inner pipe 17 during the wash operation.

In forming the cavern, a solvent, such as fresh water, is pumped down annulus 18 and the resulting solution, such as brine, formed by the washing operation removed via tubing 17. During the formation of the cavern, inner pipe 17 can be vertically moved up and down in order to facilitate the washing operation. Occasionally, the circulation of the fluid in the borehole and the cavern can be reversed. The cavern 10 resulting from the washing operation will very often have an irregular shape such as that shown in the drawing, this shape being due to the manner of circulation, presence of shale stringers, or imbedded insoluble material such as gypsum. Alternatively, the cavern can have a regular shape, such as an inverted or upright cone, or can be in the shape of a cylinder. The upper end of casing 14- can be provided with surface or product inlet pipe 19 having a flow control valve 21 therein, such as an air operated motor valve. Product line is connected to the discharge outlet of a suitable pump 22. The upper end of the inner pipe 17 can also be provided with a branched conduit or brine withdrawal pipe 23 having a similar valve 24 therein, this pipe then communicating with a brine pond or reservoir.

When it is desired to prepare the completed underground storage cavern for storage of product, the cavern, including the eductor pipe 17, is filled first with brine. The product is then pumped via conduit 19 into the upper end of the annulus 18, the resulting stored product 26 being immiscible and lighter than the pool of brine 27 forming an interface therewith. As the amount of product 26 increases in the cavern, the brine 27 is displaced upwardly to the surface via conduit 17 and then conveyed via line 23 to the brine pond or reservoir. During this operation, the interface 28 is progressively lowered and approaches the lower open end of pipe 17. It is thus seen that some means must be provided in order to prevent the product 26 from entering the lower open end of pipe 17 and cause the product to be discharged to the brine pond where a fire hazard can result.

According to this invention, the brine withdrawal line 23 is provided with a suitable orifice 29, either sides of the latter being operatively connected by suitable pres-sure sensing lines to a differential pressure regulator controller 31. The latter is operatively connected to valve 24 so as to close the same. The product inlet line 19 is operatively connected to a pressure recorder controller 32, such as a back pressure regulating controller, and the latter is operatively connected to valve 21 so as to control the same in accordance therewith. Alternatively, the pressure regulator controller 32 can also be operatively connected to a suitable conventional switch of pump 22 so as to control the operation thereof.

Referring to the alternative embodiment illustrated in FIGURE 2, the differential pressure recorder controller 31, which is operatively connected to the brine withdrawal line 23, is operatively connected to valve 21 in the product line 19, and alternatively can also be connected to the switch of pump 22 in the product line 19, so as to control the same in accordance therewith.

Referring to FIGURE 1 again, in operation, the cavern is filled by pumping the product, such as liquefied propane, via pump 22, valve 21, and conduit 19 into the upper end of annulus 18. As the cavern becomes filled with product 26, the brine 27 is displaced upwardly via conduit 17 to the surface, where it is conducted via line 23 and valve 24 to the brine pond or reservoir. During this filling operation, the valves 21 and 24 are, of course, completely open, and the interface 28 is progressively lowered in the cavern 10. Near the point in the operation when the cavern is substantially filled with product, the interface 28 will be at a position adjacent the lower open end of pipe 17 and initially a small amount of product will be discharged to the surface via line 17 along with some displaced brine. The density of the product decreases as it rises to the top of pipe 17 because of the progressively decreased head of pressure. Simultaneously, the pump 22 will increase in speed, resulting in an increase in the rate of flow of brine to the brine pond via line 23. As the product rises a short distance in the pipe 17, the pressure of the product will be released and it will vaporize. The vapor occupying a considerably larger volume than the liquid product will substantially increase the velocity of the fluid in the pipe 17 and discharge conduit 23. When the differential pressure measuring device 31 increases above a predetermined pressure, it actuates the valve 24 so as to close the same, thus preventing further discharge of product along with displaced brine to the brine reservoir. When the pressure of the product passing to the cavern 10 increases above a predetermined value, back pressure regulator 32 is actuated and it closes the valve 21 of the discharge side of the pump 22 in the product line 19. Alternatively, this pressure regulator controller 32 can be operatively adapted so as to also shut down the pump 22 after valve 21 is closed.

Referring to FIGURE 2, in operation, when the differential pressure recorder controller 31 senses the increase in differential pressure, indicative of the filling of the cavern, this device operatively closes valve 24 in the brine withdrawal line 23, and subsequently closes the valve 21 in the product line 19, and then can be operatively adapted to shut down the pump 22.

It i thus evident that the filling of the cavern can be completely automatically controlled by the practice of this invention. When operating according to this invention, the brine withdrawal line is closed as soon as a small amount of the product begins to enter the brine withdrawal line and before suflicient product has passed out of the cavern along with the brine to the brine pond.

As an example, referring again to FIGURE 1, an underground storage cavern, prepared as described by dissolving out a salt formation, having a total depth of 1600 feet and a total volume of 150,000 barrels, is provided with a 13 inch casing and a 4 inch tubing, the top of the cavern being at 1000 feet below the surface of the ground. The annulus between the casing and tubing is connected at the surface to a 4 inch product inlet line provided with an electrically operated back pressure valve operatively connected and actuated by a pressure recorder controller. The upper end of the tubing is connected at the surface to a 4 inch brine line having disposed therein an orifice plate with a 2.5 inch opening, either side of this plate being operatively connected to a suitable pressure recorder controller, such as a Barton 211 controller provided with an indicating scale and an incorporated mercoid switch, this instrument being described in Bulletin 211-1 of the Barton Instrument Corporation, Los Angeles, California. This controller is operatively connected to a suitable valve, such as an electrically operated Limitorque valve. This valve is described in Bulletin No. 215, of the Philadelphia Gear Works of Philadelphia, Pa., dated 1953.

When it is desired to completely fill the storage cavern, product, such as liquefied propane, is pumped into the annulus at a rate of 12,000 bbL/day under a pressure of 600 p.s.i.g., and brine is displaced via the tubing at a pressure of 20 p.s.i.g. When the cavern is completely filled with product, it will have a product volume of 149,500 barrels and a small amount of product will enter the lower end of the tubing and be displaced along with the brine. As this small amount of product rises to the top of the tubing, it will vaporize or expand, due to the decreasing hydrostatic head, and the differential pressure across the orifice plate in the brine line will increase. The lighter product flowing through the orifice can also cause these differential pressures to increase. As a result, the differential pressure controller, operatively connected to the opposite sides of the orifice plate in the brine line, will sense this increase in differential pressure and accordingly actuate the control mechanism which closes the valve in the brine line. This operation causes the pressure in the cavern to build up, with a consequent pressure build up in the product inlet line to that of a predetermined value above 600 p.s.i.g. Accordingly, the back pressure regulator in the product inlet line actuates the control mechanism of the Limitorque valve, closing the same, and at the same time stopping the product pump. This results in the cavern being shut in under pressure.

Various modifications and alternations of this invention will become apparent to those skilled in the art from the foregoing discussion and drawing, and it is to be understood that this invention is not necessarily limited to the aforementioned and described embodiments which illustrate only preferred embodiments of this invention.

I claim:

1. A method of controlling the filling of an underground storage cavern with a fluid product, said cavern comprising an underground cavity defined by an impermeable formation and an access bore extending from said cavity to the ground surface, said cavern normally containing a displacing liquid heavier than and immiscible with said product with an interface formed therebetween, said cavern being provided with a tubing depending within said access bore and communicating with said cavity at its lower end, said tubing and said access bore defining a space therebetween, the lower end of said tubing being adjacent the bottom of said cavern at a point normally below said interface, said method comprising the steps of introducing the product normally gaseous at atmospheric pressure in said cavern via said space between said tubing and access bore at a constant initial flow rate so as to displace said liquid in said cavern, withdrawing the displaced said liquid from said cavern via said tubing, continuously measuring the differential pressure across an orifice located in said tubing at a point above ground during the withdrawal of said liquid, ceasing the withdrawal of said liquid when said diiierential pressure indicates a predetermined flow rate higher than said initial flow rate, and ceasing the introduction of said product into said cavern, whereby the discharge of any substantial amount of said product through said tubing is prevented.

2. A method of controlling the filling of an underground storage cavern with a fluid product, said cavern comprising a cavity having a relatively large diameter defined by an impermeable formation and an access bore of relatively smaller diameter extending from said cavity to the ground surface, said cavern normally containing a displacing liquid heavier than and immiscible with said product with an interface forming therebetween, said cavern being provided with a tubing which together with said access bore defines an annular space communicating with said cavity, the lower end of said tubing being adjacent the bottom of said cavern at a point normally below said interface, said method comprising the steps of introducing product normally gaseous at atmospheric pressure in said cavern via the upper end of said annulus at a constant initial flow rate so as to displace said liquid in said cavern, withdrawing the displaced said liquid from said cavern via said tubing, continuously measuring the flow rate of the withdrawn liquid passing thru an orifice located in said tubing at a point above ground, ceasing the withdrawal of said liquid when the flow rate through said orifice in said tubing indicates a predetermined flow rate higher than said initial flow rate which is indicative of the presence of said product in said tubing, and ceasing the introduction of said product whereby the discharge of any substantial amount of said product through said tubing is prevented.

3. The method according to claim 2 wherein said liquid is brine and said product is liquefied petroleum gas.

4. The method according to claim 2 wherein said liquid is brine and said product is liquefied propane.

5. The method according to claim 2 wherein said liquid is brine and said product is liquefied butane.

6. The method according to claim 2 wherein said liquid is brine and said product is gaseous ethylene.

7. The method of claim 2 further comprising the step of ceasing the introduction of said product when the pressure of said introduced product reaches a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 127,917 Painter June 11, 1872 2,661,062 Edholm Dec. 1, 1953 2,772,564 Dougherty Dec. 4, 1956 2,787,125 Benz Apr. 2, 1957 2,803,432 Teichmann et al Aug. 20, 1957 2,928,247 Hubbell Mar. 15, 1960 2,942,424 Koble June 28, 1960 2,950,601 Wightman Aug. 30, 1960 FOREIGN PATENTS 795,096 Great Britain May 14, 1958 OTHER REFERENCES Petroleum Refiner magazine, July 1954, page 111. 

